Mail Routing Fails

We have more than 50 servers in our network and most are working fine.However we have 4 servers that intermittently get:

“Router: No messages transferred to xxxxxxxx/xxxx via Notes: The server is not responding. The server may be down or you may be experiencing network problems. Contact your system administrator if this problem persists.”

If I set passthru connections everything works fine.

If I do a TCP trace route - it works.

If I do a TCPIP port trace from the Notes client - it connects to the server via the passthru connection but it fails directly to the server IP address, if the passthru record is not there the trace fails to both the IP address and the server name.

Our comm guys are telling me that everything is fine, they cannot find anything wrong.

If I didn’t have the print screens and see this first hand I would think I was nuts too.

What can cause this type of routing error?

Thanks in advance…